Chapter 2: Physical Activity Has Many Health Benefits

All Americans should be regularly physically active to improve overall
health and fitness and to prevent many adverse health outcomes. The benefits of
physical activity occur in generally healthy people, in people at risk of
developing chronic diseases, and in people with current chronic conditions or
disabilities. This chapter gives an overview of research findings on physical
activity and health. The box below provides a summary of these benefits.

Physical activity affects many health conditions, and the specific
amounts and types of activity that benefit each condition vary. In developing
public health guidelines, the challenge is to integrate scientific information
across all health benefits and identify a critical range of physical activity
that appears to have an effect across the health benefits. One consistent
finding from research studies is that once the health benefits from physical
activity begin to accrue, additional amounts of activity provide additional
benefits.

Although some health benefits seem to begin with as little as 60
minutes (1 hour) a week, research shows that a total amount of 150 minutes (2
hours and 30 minutes) a week of moderate-intensity aerobic activity, such as
brisk walking, consistently reduces the risk of many chronic diseases and other
adverse health outcomes.

Examining the Relationship Between Physical Activity and Health

In many studies covering a wide range of issues, researchers have
focused on exercise, as well as on the more broadly defined
concept of physical activity. Exercise is a form of physical activity that is
planned, structured, repetitive, and performed with the goal of improving
health or fitness. So, although all exercise is physical activity, not all
physical activity is exercise.

Studies have examined the role of physical activity in many
groups—men and women, children, teens, adults, older adults, people with
disabilities, and women during pregnancy and the postpartum period. These
studies have focused on the role that physical activity plays in many health
outcomes, including:

Risk factors for disease, such as high blood pressure and high blood
cholesterol;

Physical fitness, such as aerobic
capacity, and muscle strength and endurance

Functional capacity (the ability to engage in activities needed for
daily living);

Mental health, such as depression and cognitive function; and

Injuries or sudden heart attacks.

These studies have also prompted questions as to what type and how much
physical activity is needed for various health benefi ts. To answer this
question, investigators have studied three main kinds of physical activity:
aerobic, muscle-strengthening, and bonestrengthening. Investigators have also
studied balance and fl exibility activities. These latter two activities are
addressed in Chapters 4, 5, and 6.

Most health benefits occur with at least 150 minutes a week of
moderate-intensity physical activity, such as brisk walking. Additional
benefits occur with more physical activity.

Both aerobic (endurance) and muscle-strengthening (resistance)
physical activity are beneficial.

Health benefits occur for children and adolescents, young and
middle-aged adults, older adults, and those in every studied racial and ethnic
group.

The health benefits of physical activity occur for people with
disabilities.

The benefits of physical activity far outweigh the possibility of
adverse outcomes.

Aerobic Activity

In this kind of physical activity (also called an endurance
activity or cardio activity), the body's large muscles move in a
rhythmic manner for a sustained period of time. Brisk walking, running,
bicycling, jumping rope, and swimming are all examples.

Aerobic activity causes a person's heart to beat faster than usual.

Aerobic physical activity has three components:

Intensity, or how hard a person works to do the
activity. The intensities most often examined are moderate intensity
(equivalent in effort to brisk walking) and vigorous intensity (equivalent in
effort to running or jogging);

Frequency, or how often a person does aerobic
activity; and

Duration, or how long a person does an activity in
any one session.

Although these components make up a physical activity profile, research
has shown that the total amount of physical activity (minutes of
moderate–intensity physical activity, for example) is more important for
achieving health benefits than is any one component (frequency, intensity, or
duration).

Muscle-Strengthening Activity

This kind of activity, which includes resistance
training and lifting weights, causes the body's muscles to work or
hold against an applied force or weight. These activities often involve
relatively heavy objects, such as weights, which are lifted multiple times to
train various muscle groups. Muscle-strengthening activity can also be done by
using elastic bands or body weight for resistance (climbing a tree or doing
push-ups, for example).

Muscle-strengthening activity also has three components:

Intensity, or how much weight or force is used
relative to how much a person is able to lift;

Frequency, or how often a person does muscle
strengthening activity; and

Repetitions, or how many times a person lifts a
weight (analogous to duration for aerobic activity). The effects of
muscle-strengthening activity are limited to the muscles doing the work. It's
important to work all the major muscle groups of the body: the legs, hips,
back, abdomen, chest, shoulders, and arms.

Bone-Strengthening Activity

This kind of activity (sometimes called weight-bearing or
weight-loading activity) produces a force on the bones that promotes bone
growth and strength. This force is commonly produced by impact with the ground.
Examples of bone-strengthening activity include jumping jacks, running, brisk
walking, and weight-lifting exercises. As these examples illustrate,
bone-strengthening activities can also be aerobic and muscle strengthening.

The Health Benefits of Physical Activity

Studies clearly demonstrate that participating in regular physical
activity provides many health benefits. These benefits are summarized in the
accompanying table. Many conditions affected by physical activity occur with
increasing age, such as heart disease and cancer. Reducing risk of these
conditions may require years of participation in regular physical activity.
However, other benefits, such as increased cardiorespiratory
fitness, increased muscular strength, and decreased depressive
symptoms and blood pressure, require only a few weeks or months of
participation in physical activity.

Health Benefits Associated With Regular Physical Activity

Children and Adolescents

Strong evidence

Improved cardiorespiratory and muscular fitness

Improved bone health

Improved cardiovascular and metabolic health biomarkers

Favorable body composition

Moderate evidence

Reduced symptoms of depression

Adults and Older Adults

Strong evidence

Lower risk of early death

Lower risk of coronary heart disease

Lower risk of stroke

Lower risk of high blood pressure

Lower risk of adverse blood lipid profile

Lower risk of type 2 diabetes

Lower risk of metabolic syndrome

Lower risk of colon cancer

Lower risk of breast cancer

Prevention of weight gain

Weight loss, particularly when combined with reduced calorie
intake

Improved cardiorespiratory and muscular fitness

Prevention of falls

Reduced depression

Better cognitive function (for older adults)

Moderate to strong evidence

Better functional health (for older adults)

Reduced abdominal obesity

Moderate evidence

Lower risk of hip fracture

Lower risk of lung cancer

Lower risk of endometrial cancer

Weight maintenance after weight loss

Increased bone density

Improved sleep quality

Note: The Advisory Committee rated the
evidence of health benefits of physical activity as strong, moderate, or weak.
To do so, the Committee considered the type, number, and quality of studies
available, as well as consistency of findings across studies that addressed
each outcome. The Committee also considered evidence for causality and
dose response in assigning the strength-of-evidence
rating.

The Beneficial Effects of Increasing Physical Activity: It's About
Overload, Progression, and Specificity

Overload is the physical stress placed on the body
when physical activity is greater in amount or intensity than usual. The body's
structures and functions respond and adapt to these stresses. For example,
aerobic physical activity places a stress on the cardiorespiratory system and
muscles, requiring the lungs to move more air and the heart to pump more blood
and deliver it to the working muscles. This increase in demand increases the
efficiency and capacity of the lungs, heart, circulatory system, and exercising
muscles. In the same way, muscle–strengthening and bone-strengthening
activities overload muscles and bones, making them stronger.

Progression is closely tied to overload. Once a
person reaches a certain fitness level, he or she progresses to higher levels
of physical activity by continued overload and adaptation. Small, progressive
changes in overload help the body adapt to the additional stresses while
minimizing the risk of injury.

Specificity means that the benefits of physical
activity are specific to the body systems that are doing the work. For example,
aerobic physical activity largely benefits the body's cardiovascular system.

The health benefits of physical activity are seen in children and
adolescents, young and middle-aged adults, older adults, women and men, people
of different races and ethnicities, and people with disabilities and chronic
conditions. The health benefits of physical activity are generally independent
of body weight. Adults of all sizes and shapes gain health and fitness benefits
by being habitually physically active. The benefits of physical activity also
outweigh the risk of injury and sudden heart attacks, two concerns that prevent
many people from becoming physically active.

The following sections provide more detail on what is known from
research studies about the specific health benefits of physical activity and
how much physical activity is needed to get the health benefits.

Premature Death

Strong scientific evidence shows that physical activity reduces the
risk of premature death (dying earlier than the average age of death for a
specific population group) from the leading causes of death, such as heart
disease and some cancers, as well as from other causes of death. This effect is
remarkable in two ways:

First, only a few lifestyle choices have as large an effect on
mortality as physical activity. It has been estimated that people who are
physically active for approximately 7 hours a week have a 40 percent lower risk
of dying early than those who are active for less than 30 minutes a week.

Second, it is not necessary to do high amounts of activity or
vigorous-intensity activity to reduce the risk of premature death. Studies show
substantially lower risk when people do 150 minutes of at least
moderate-intensity aerobic physical activity a week.

Research clearly demonstrates the importance of avoiding inactivity.
Even low amounts of physical activity reduce the risk of dying prematurely. As
the figure on page 11 shows, the most dramatic difference in risk is seen
between those who are inactive (30 minutes a week) and those with low levels of
activity (90 minutes or 1 hour and 30 minutes a week). The relative
risk of dying prematurely continues to be lower with higher levels of
reported moderate- or vigorous-intensity leisure-time physical activity.

All adults can gain this health benefit of physical activity. Age,
race, and ethnicity do not matter. Men and women younger than 65 years as well
as older adults have lower rates of early death when they are physically active
than when they are inactive. Physically active people of all body weights
(normal weight, overweight, obese) also have lower rates of early death than do
inactive people.

The Risk of Dying Prematurely Declines as People Become Physically
Active

Minutes per Week of Moderate- or
Vigorous-Intensity Physical Activity

The Risk of Dying Prematurely Declines as People Become Physically
Active—Data Points

Minutes per Week of Moderate- or
Vigorous-Intensity Physical Activity

Relative Risk

30

1

90

0.8

180

0.73

330

0.64

420

0.615

Cardiorespiratory Health

The benefits of physical activity on cardiorespiratory health are some
of the most extensively documented of all the health benefits.
Cardiorespiratory health involves the health of the heart, lungs, and blood
vessels.

Heart diseases and stroke are two of the leading causes of death in the
United States. Risk factors that increase the likelihood of cardiovascular
diseases include smoking, high blood pressure (called hypertension), type 2
diabetes, and high levels of certain blood lipids (such as low-density
lipoprotein, or LDL, cholesterol). Low cardiorespiratory fitness also is a risk
factor for heart disease.

People who do moderate- or vigorous-intensity aerobic physical activity
have a significantly lower risk of cardiovascular disease than do inactive
people. Regularly active adults have lower rates of heart disease and stroke,
and have lower blood pressure, better blood lipid profiles, and fitness.
Significant reductions in risk of cardiovascular disease occur at activity
levels equivalent to 150 minutes a week of moderate-intensity physical
activity. Even greater benefits are seen with 200 minutes (3 hours and 20
minutes) a week. The evidence is strong that greater amounts of physical
activity result in even further reductions in the risk of cardiovascular
disease.

Everyone can gain the cardiovascular health benefits of physical
activity. The amount of physical activity that provides favorable
cardiorespiratory health and fitness outcomes is similar for adults of various
ages, including older people, as well as for adults of various races and
ethnicities. Aerobic exercise also improves cardiorespiratory fitness in
individuals with some disabilities, including people who have lost the use of
one or both legs and those with multiple sclerosis, stroke, spinal cord injury,
and cognitive disabilities.

Moderate-intensity physical activity is safe for generally healthy
women during pregnancy. It increases cardiorespiratory fitness without
increasing the risk of early pregnancy loss, preterm delivery, or low birth
weight. Physical activity during the postpartum period also improves
cardiorespiratory fitness.

Metabolic Health

Regular physical activity strongly reduces the risk of developing type
2 diabetes as well as the metabolic syndrome. The metabolic syndrome is defined
as a condition in which people have some combination of high blood pressure, a
large waistline (abdominal obesity), an adverse blood lipid profile (low levels
of high-density lipoprotein [HDL] cholesterol, raised triglycerides), and
impaired glucose tolerance.

People who regularly engage in at least moderate intensity aerobic
activity have a significantly lower risk of developing type 2 diabetes than do
inactive people. Although some experts debate the usefulness of defining the
metabolic syndrome, good evidence exists that physical activity reduces the
risk of having this condition, as defined in various ways. Lower rates of these
conditions are seen with 120 to 150 minutes (2 hours to 2 hours and 30 minutes)
a week of at least moderate-intensity aerobic activity. As with cardiovascular
health, additional levels of physical activity seem to lower risk even further.
In addition, physical activity helps control blood glucose levels in persons
who already have type 2 diabetes.

Physical activity also improves metabolic health in youth. Studies find
this effect when young people participate in at least 3 days of vigorous
aerobic activity a week. More physical activity is associated with improved
metabolic health, but research has yet to determine the exact amount of
improvement.

Obesity and Energy Balance

Overweight and obesity occur when fewer calories are expended,
including calories burned through physical activity, than are taken in through
food and beverages. Physical activity and caloric intake both must be
considered when trying to control body weight. Because of this role in energy
balance, physical activity is a critical factor in determining whether a person
can maintain a healthy body weight, lose excess body weight, or maintain
successful weight loss. People vary a great deal in how much physical activity
they need to achieve and maintain a healthy weight. Some need more physical
activity than others to maintain a healthy body weight, to lose weight, or to
keep weight off once it has been lost.

Strong scientific evidence shows that physical activity helps people
maintain a stable weight over time. However, the optimal amount of physical
activity needed to maintain weight is unclear. People vary greatly in how much
physical activity results in weight stability. Many people need more than the
equivalent of 150 minutes of moderate-intensity activity a week to maintain
their weight.

Over short periods of time, such as a year, research shows that it is
possible to achieve weight stability by doing the equivalent of 150 to 300
minutes (5 hours) a week of moderate-intensity walking at about a 4
mile-an-hour pace. Muscle-strengthening activities may help promote weight
maintenance, although not to the same degree as aerobic activity.

People who want to lose a substantial (more than 5 percent of body
weight) amount of weight and people who are trying to keep a significant amount
of weight off once it has been lost need a high amount of physical activity
unless they also reduce their caloric intake. Many people need to do more than
300 minutes of moderate-intensity activity a week to meet weight–control
goals.

Regular physical activity also helps control the percentage of body fat
in children and adolescents. Exercise training studies with overweight and
obese youth have shown that they can reduce their body fatness by participating
in physical activity that is at least moderate intensity on 3 to 5 days a week,
for 30 to 60 minutes each time.

Musculoskeletal Health

Bones, muscles, and joints support the body and help it move. Healthy
bones, joints, and muscles are critical to the ability to do daily activities
without physical limitations.

Preserving bone, joint, and muscle health is essential with increasing
age. Studies show that the frequent decline in bone density that happens during
aging can be slowed with regular physical activity. These effects are seen in
people who participate in aerobic, muscle–strengthening, and
bone-strengthening physical activity programs of moderate or vigorous
intensity. The range of total physical activity for these benefits varies
widely. Important changes seem to begin at 90 minutes a week and continue up to
300 minutes a week.

Hip fracture is a serious health condition that can have life-changing
negative effects for many older people. Physically active people, especially
women, appear to have a lower risk of hip fracture than do inactive people.
Research studies on physical activity to prevent hip fracture show that
participating in 120 to 300 minutes a week of physical activity that is of at
least moderate intensity is associated with a reduced risk. It is unclear,
however, whether activity also lowers risk of fractures of the spine or other
important areas of the skeleton.

The bottom line is that the health benefits of physical activity far
outweigh the risks of adverse events for almost everyone.

Building strong, healthy bones is also important for children and
adolescents. Along with having a healthy diet that includes adequate calcium
and vitamin D, physical activity is critical for bone development in children
and adolescents. Bone-strengthening physical activity done 3 or more days a
week increases bone-mineral content and bone density in youth.

Regular physical activity also helps people with arthritis or other
rheumatic conditions affecting the joints. Participation in 130 to 150 minutes
(2 hours and 10 minutes to 2 hours and 30 minutes) a week of
moderate-intensity, low-impact physical activity improves pain management,
function, and quality of life. Researchers don't yet know whether participation
in physical activity, particularly at low to moderate intensity, reduces the
risk of osteoarthritis. Very high levels of physical activity, however, may
have extra risks. People who participate in very high levels of physical
activity, such as elite or professional athletes, have a higher risk of hip and
knee osteoarthritis, mostly due to the risk of injury involved in competing in
some sports.

Progressive muscle-strengthening activities increase or preserve muscle
mass, strength, and power. Higher amounts (through greater frequency or higher
weights) improve muscle function to a greater degree. Improvements occur in
younger and older adults. Resistance exercises also improve muscular strength
in persons with such conditions as stroke, multiple sclerosis, cerebral palsy,
spinal cord injury, and cognitive disability. Though it doesn't increase muscle
mass in the same way that muscle-strengthening activities do, aerobic activity
may also help slow the loss of muscle with aging.

Functional Ability and Fall Prevention

Functional ability is the capacity of a person to perform tasks or
behaviors that enable him or her to carry out everyday activities, such as
climbing stairs or walking on a sidewalk. Functional ability is key to a
person's ability to fulfill basic life roles, such as personal care, grocery
shopping, or playing with the grandchildren. Loss of functional ability is
referred to as functional limitation.

Middle-aged and older adults who are physically active have lower risk
of functional limitations than do inactive adults. It appears that greater
physical activity levels can further reduce risk of functional limitations.

Older adults who already have functional limitations also benefit from
regular physical activity. Typically, studies of physical activity in adults
with functional limitations tested a combination of aerobic and muscle
strengthening activities, making it difficult to assess the relative importance
of each type of activity. However, both types of activity appear to provide
benefit.

In older adults at risk of falls, strong evidence shows that regular
physical activity is safe and reduces this risk. Reduction in falls is seen for
participants in programs that include balance and moderate-intensity
muscle-strengthening activities for 90 minutes a week plus moderate-intensity
walking for about an hour a week. It's not known whether different combinations
of type, amount, or frequency of activity can reduce falls to a greater degree.
Tai chi exercises also may help prevent falls.

Cancer

Physically active people have a significantly lower risk of colon
cancer than do inactive people, and physically active women have a
significantly lower risk of breast cancer. Research shows that a wide range of
moderate-intensity physical activity—between 210 and 420 minutes a week (3
hours and 30 minutes to 7 hours)—is needed to significantly reduce the
risk of colon and breast cancer; currently, 150 minutes a week does not appear
to provide a major benefit. It also appears that greater amounts of physical
activity lower risks of these cancers even further, although exactly how much
lower is not clear.

Although not definitive, some research suggests that the risk of
endometrial cancer in women and lung cancers in men and women also may be lower
among those who are regularly active compared to those who are inactive.

Finally, cancer survivors have a better quality of life and improved
physical fitness if they are physically active, compared to survivors who are
inactive.

Mental Health

Physically active adults have lower risk of depression and cognitive
decline (declines with aging in thinking, learning, and judgment skills).
Physical activity also may improve the quality of sleep. Whether physical
activity reduces distress or anxiety is currently unclear.

Mental health benefits have been found in people who do aerobic or a
combination of aerobic and muscle– strengthening activities 3 to 5 days a
week for 30 to 60 minutes at a time. Some research has shown that even lower
levels of physical activity also may provide some benefits.

Regular physical activity appears to reduce symptoms of anxiety and
depression for children and adolescents. Whether physical activity improves
self-esteem is not clear.

Adverse Events

Some people hesitate to become active or increase their level of
physical activity because they fear getting injured or having a heart attack.
Studies of generally healthy people clearly show that moderate-intensity
physical activity, such as brisk walking, has a low risk of such
adverse events.

The risk of musculoskeletal injury increases with the total amount of
physical activity. For example, a person who regularly runs 40 miles a week has
a higher risk of injury than a person who runs 10 miles each week. However,
people who are physically active may have fewer injuries from other causes,
such as motor vehicle collisions or work-related injuries. Depending on the
type and amount of activity that physically active people do, their overall
injury rate may be lower than the overall injury rate for inactive people.

Participation in contact or collision sports, such as soccer or
football, has a higher risk of injury than participation in non-contact
physical activity, such as swimming or walking. However, when performing the
same activity, people who are less fit are more likely to be injured than
people who are fitter.

Cardiac events, such as a heart attack or sudden death during physical
activity, are rare. However, the risk of such cardiac events does increase when
a person suddenly becomes much more active than usual. The greatest risk occurs
when an adult who is usually inactive engages in vigorous-intensity activity
(such as shoveling snow). People who are regularly physically active have the
lowest risk of cardiac events both while being active and overall.

The bottom line is that the health benefits of physical activity far
outweigh the risks of adverse events for almost everyone.